Quantitative structure-odor relationships of aliphatic esters using topological indices

Quantitative structure-activity relationships (QSAR) were used in this study to relate the structural parameters (electronic, topological, etc.) to the odor of 27 aliphatic esters previously evaluated by Rossiter. Rossiter used the Hansch approach, principal component analysis and comparative molecular field analysis (CoMFA) to predict the odor of these esters. Different structural parameters were selected, such as topological, physicochemical, and quantum-chemical indices, to find an equation to predict the molecular factors that determine the fruit odor of these compounds and to compare such results with those obtained by Rossiter. Two significant correlation equations were obtained with the following molecular descriptors: one with the electrotopological-state index related to the carbon atom of the carbonyl group (S-C=O), the Kappa index (K-2), and the topological-state index related to the oxygen on the alcoholic side of the molecule (T-O-), and the other with 2K, S-C=O, and the energy of the highest occupied molecular orbital (E-HOMO) The model found had a good predictive ability as established by cross-validation r(cv)(2) values and thus can he used to help in the prediction of odor of similar compounds. This method is simplier than the methods used by Rossiter and represents a reliable QSAR alternative in predicting the fruit odor of such aliphatic esters.